"Do you speak Spanish in school?"
Translation:¿Hablas español en la escuela?
It would appear that from what I have seen, experienced and read, if the word is being used as a noun it has a "prefix" ie: la, de, el and so on. If the word is being used to describe such as an adjective, no "prefix" is used and it would be grammatically incorrect. That is just how Spanish is in general.
It doesn't mean a particular school. It's the translation of "at school", meaning in the school you attend, so Spanish use the expression "en la escuela", and it makes sense, considering you talk about the school you are attending.
Spanish and English use different construction, to mean the same thing.
Note that, with a different context, it could be a specified school. There's a bar and a school in my town, but I prefer to be in the school. = here specified building.
En la escuela in Spanish, and in the school in English.
Here's a link that helped me clarify rules for using Spanish articles: https://www.thoughtco.com/use-and-omission-of-definite-article-3078144
Im not sure what the question was for your previous task but ill say “La escuela es importante” is a correct translation of “school is important.” If you were marked wrong i think there was probably a slight spelling mistake. In a sentence where a regular noun directly follows the word “en” always use an article before the noun. Im not a native speaker but i havent found a sentence where this doesnt hold true.